Coil arrays for parallel imaging in magnetic resonance imaging

ABSTRACT

A partially parallel acquisition RF coil array for imaging a sample includes at least a first, a second and a third coil adapted to be arranged circumambiently about the sample and to provide both contrast data and spatial phase encoding data.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional patentapplication Ser. No. 60/296,885 filed Jun. 8, 2001.

BACKGROUND OF THE INVENTION

The present invention relates to magnetic resonance imaging (MRI)systems, and particularly to the radio frequency (RF) coils used in suchsystems.

Magnetic resonance imaging (MRI) utilizes hydrogen nuclear spins of thewater molecules in the human body or other tissue, which are polarizedby a strong, uniform, static magnetic field generated by a magnet(referred to as B₀—the main magnetic field in MRI physics). Themagnetically polarized nuclear spins generate magnetic moments in thehuman body. The magnetic moments point in the direction of the mainmagnetic field in a steady state, and produce no useful information ifthey are not disturbed by any excitation.

The generation of nuclear magnetic resonance (NMR) signal for MRI dataacquisition is achieved by exciting the magnetic moments with a uniformradio frequency (RF) magnetic field (referred to as the B₁ field or theexcitation field). The B₁ field is produced in the imaging region ofinterest by an RF transmit coil which is driven by a computer-controlledRF transmitter with a power amplifier. During the excitation, thenuclear spin system absorbs magnetic energy, and its magnetic momentsprecess around the direction of the main magnetic field. After theexcitation, the precessing magnetic moments will go through a process offree induction decay, emitting their absorbed energy and then returningto the steady state. During the free induction decay, NMR signals aredetected by the use of a receive RF coil, which is placed in thevicinity of the excited volume of the human body. The NMR signal is aninduced electrical motive force (voltage), or current, in the receive RFcoil that has been induced by the flux change over some time period dueto the relaxation of precessing magnetic moments in the human tissue.This signal provides the contrast information of the image. The receiveRF coil can be either the transmit coil itself, or an independentreceive-only RF coil. The NMR signal is used for producing magneticresonance images by using additional pulsed magnetic gradient fields,which are generated by gradient coils integrated inside the main magnetsystem. The gradient fields are used to spatially encode the signals andselectively excite a specific volume of the human body. There areusually three sets of gradient coils in a standard MRI system, whichgenerate magnetic fields in the same direction of the main magneticfield, varying linearly in the imaging volume.

In MRI, it is desirable for the excitation and reception to be spatiallyuniform in the imaging volume for better image uniformity. In a standardMRI system, the best excitation field homogeneity is usually obtained byusing a whole-body volume RF coil for transmission. The whole-bodytransmit coil is the largest RF coil in the system. A large coil,however, produces lower signal-to-noise ratio (S/N) if it is also usedfor reception, mainly because of its greater distance from thesignal-generating tissues being imaged. Since a high signal-to-noiseratio is the most desirable factor in MRI, special-purpose coils areused for reception to enhance the S/N ratio from the volume of interest.

In practice, a well-designed specialty RF coil should have the followingfunctional properties: high S/N ratio, good uniformity, high unloadedquality factor (Q) of the resonance circuit, and high ratio of theunloaded to loaded Q factors. In addition, the coil device must bemechanically designed to facilitate patient handling and comfort, and toprovide a protective barrier between the patient and the RF electronics.Another way to increase the S/N is by quadrature reception. In thismethod, NMR signals are detected in two orthogonal directions, which arein the transverse plane or perpendicular to the main magnetic field. Thetwo signals are detected by two independent individual coils which coverthe same volume of interest. With quadrature reception, the S/N can beincreased by up to ✓2 over that of the individual linear coils.

To cover a large field-of-view, while maintaining the S/N characteristicof a small and conformal coil, a linear surface coil array technique wascreated to image the entire human spines (U.S. Pat. No. 4,825,162).Subsequently, other linear surface array coils were used for C.L. spineimaging, such as the technique described in U.S. Pat. No. 5,198,768.These two devices consist of an array of planar linear surface coilelements. These coil systems do not work well for imaging deep tissues,such as the blood vessels in the lower abdomen, due to sensitivitydrop-off away from the coil surface.

To image the lower extremities, quadrature phased array coils have beenutilized such as described in U.S. Pat. Nos. 5,430,378 and 5,548,218.The first quadrature phased array coil, images the lower extremities byusing two orthogonal linear coil arrays: six planar loop coil elementsplaced in the horizontal plane and underneath the patient and six planarloop coil elements placed in the vertical plane and in between the legs.Each linear coil array functions in a similar way as described in U.S.Pat. No. 4,825,162 (Roemer). The second quadrature phased array coil(Lu) was designed to image the blood vessels from the pelvis down. Thisdevice also consists of two orthogonal linear coil arrays extending inthe head-to-toe direction: a planar array of loop coil elementslaterally centrally located on top of the second array of butterfly coilelements. The loop coils are placed immediately underneath the patientand the butterfly coils are wrapped around the patient. Again, eachlinear coil array functions in a similar way as described in U.S. Pat.No. 4,825,162.

In MRI, gradient coils are routinely used to give phase-encodinginformation to a sample to be imaged. To obtain an image, it is requiredthat all the data points in a so-called “k-space” (i.e., frequencyspace) must be collected. Recently, there have been developments wheresome of the data points in k-space are intentionally skipped and at thesame time use the intrinsic sensitivity information of RF receive coilsas the phase-encoding information for those skipped data points. Thisaction takes place simultaneously, and thus is referred to as partiallyparallel imaging or partially parallel acquisition (PPA). By collectingmultiple data points simultaneously, it requires less time to acquirethe same amount of data, when compared with the conventionalgradient-only phase-encoding approach. The time savings can be used toreduce total imaging time, in particular, for the applications in whichcardiac or respiratory motions in tissues being imaged become concerns,or to collect more data to achieve better resolution or S/N.SiMultaneous Acquisition of Spatial Harmonics, SMASH, (U.S. Pat. No.5,910,728 and “Simultaneous Acquisition of Spatial Harmonics (SMASH):Fast Imaging with Radiofrequency Coil Arrays,” Daniel K. Sodickson andWarren J. Manning, Magnetic Resonance in Medicine 38:591–603 (1997),both incorporated herein by reference) and “SENSE: Sensitivity Encodingfor Fast MRI,” Klaas P. Pruessmann, et al., Magnetic Resonance inMedicine 42:952–962 (1999, also incorporated by reference, are basicallytwo methods of PPA. SMASH takes advantage of the parallel imaging byskipping phase encode lines that yield decreasing the Field-of-View(FOV) in the phase-encoding direction and uses coils (e.g., coil arrays)together with reconstruction techniques to fill in the missing datapoints in k-space. SENSE, on the other hand, is a technique thatutilizes a reduced FOV in the read direction, resulting an aliased imagethat is then unfolded in x-space (i.e., real space), while using the RFcoil sensitivity information, to obtain a true corresponding image.Here, we make use of phase difference between signals from multiplecoils to skip phase encoding steps. By skipping some of the phaseencoding steps, one can achieve speeding up imaging process by areduction factor R. Theoretically speaking, the factor R should equalthe number of independent coils/arrays. In the SENSE approach, the SIRis defined as:SNR _(SENSE) =SNR _(FULL) /{g✓R}where SNR_(FULL) is the S/N achievable when all the phase encoding stepsare collected by traditional gradient phase encoding scheme. SNR_(SENSE)is optimized when the geometry factor g equals 1. To obtain g of 1,traditional decoupling techniques such as overlapping nearest neighborelements to null the mutual inductance between them shall not apply, ashave been reported by others.

SENSE and SMASH or a hybrid approach of both demand a new type of designrequirements in RF coil design. In SMASH, the primary criterion for thearray is that it be capable of generating sinusoids whose wavelengthsare on the order of the FOV. This is how the target FOV along the phaseencoding direction for the array is determined. Conventional arraydesigns can incorporate element and array dimensions that will giveoptimal S/N for the object of interest. In addition, users ofconventional arrays are free to choose practically any FOV, as long assevere aliasing artifacts are not a problem. In contrast, when usingSMASH, the size of the array determines the approximate range of FOVsthat can be used in the imaging experiment. This then determines theapproximate element dimensions, assuming complete coverage of the FOV isdesired, as in most cases. In SENSE, the method is based upon the factthat the sensitivity of a RF receiver coil generally has aphase-encoding effect complementary to those achieved by linear fieldgradients. For SENSE imaging, the elements of a coil array should besmaller than for common phased-array imaging, resulting in a trade-offbetween basic noise and geometry factor, and adjacent coil elementsshould not overlap for a net gain in S/N due to the improved geometryfactor when using SENSE.

For PPA applications, different types of RF coils or arrays have beenused so far. However, most of them are based upon “traditional” RF coildesign requirements, thus remain within the conventional coil designscheme. It has been reported, however, that since the phase informationof B₁ of a receive coil is very important when SENSE applications aredemanded, for example, new coil design techniques such asnon-overlapping adjacent coil elements may be necessary for betterdefinition of the individual phase information associated with each RFcoil used in an array, unlike traditional design scheme where twoadjacent coils elements are overlapped to null the mutual inductancebetween the elements (U.S. Pat. No. 4,825,162). Without overlap, thecoupling may be increased, but there is a net gain in S/N due to theimproved geometry factor when using SENSE. As stated in the above, theuse of smaller coil-elements than those for conventional imaging resultsin a trade-off between basic noise and geometry factor.

SUMMARY OF THE INVENTION

A partially parallel acquisition RF coil array for imaging a sampleincludes at least a first, a second and a third coil adapted to bearranged circumambiently about the sample and to provide both contrastdata and spatial phase encoding data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is plan and elevation views of a schematic diagram of exemplarycircular, rectangular or arbitrary-shaped loop coils.

FIG. 2 is plan and elevation views of a schematic diagram of exemplarysaddle/“Figure 8” coils.

FIG. 3 is plan views of a schematic diagram of exemplary saddle-trainand “Figure 8”-train coils.

FIG. 4 is perspective and elevation views of a schematic diagram of anexemplary ladder multi-mode coil or half-bird cage coil.

FIG. 5 is a plan view of a schematic diagram of an exemplary “H”multi-mode coil.

FIG. 6 is plan views of a schematic diagram of exemplary mode-controlledloop pair coils (MCLP coils) (connection between two loops can be arigid/flexible coaxial cable, balanced transmission line type of cablesuch as 300 ohm TV cable, or can be etched strip line transmission lineswith high characteristic impedance, greater or equal to 50 ohms, forexample).

FIG. 7 is an elevation view of a schematic diagram of a first exemplarycoil array according to the invention.

FIG. 8 is an elevation view of a schematic diagram of a second exemplarycoil array according to the invention.

FIG. 9 is an elevation view of a schematic diagram of a third exemplarycoil array according to the invention.

FIG. 10 is an elevation view of a schematic diagram of a fourthexemplary coil array according to the invention.

FIG. 11 is an elevation view of a schematic diagram of a fifth exemplarycoil array according to the invention.

FIG. 12 is an elevation view of a schematic diagram of a sixth exemplarycoil array according to the invention.

FIG. 13 is an elevation view of a schematic diagram of a seventhexemplary coil array according to the invention.

FIG. 14 is an elevation view of a schematic diagram of an eighthexemplary coil array according to the invention.

FIG. 15 is a plan view of a schematic diagram of a ninth exemplary coilarray according to the invention.

FIG. 16 is an elevation view of a schematic diagram of a tenth exemplarycoil array according to the invention.

FIG. 17 is a plan view of a schematic diagram of an eleventh exemplarycoil array according to the invention.

FIG. 18 is a plan view of a schematic diagram of a twelfth exemplarycoil array according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As is seen from the equation above, we loose S/N intrinsically when wetry to reduce the imaging time. Thus, to compensate for S/N loss, wedesign the size of each element smaller than that of conventional arrayelements. We also increase the total number of elements to cover thevolume of interest (which may be constrained by the maximum availablenumber of receiver channels).

The present invention provides an improved and advanced volume andsurface coil array that covers a large field-of-view while providinggreater S/N and can be used as a PPA targeted coil for imaging a largevolume such as head, abdomen or heart.

The present invention may also employ various combinations of coilsdistributed not only in circumambient directions but also in the zdirection and provide better S/N for the torso and cardiac imaging ascompared with a conventional torso/cardiac coil.

The basic building blocks of the present invention are the well-knowncoil configurations of FIGS. 1 through 6.

FIG. 1 shows a circular, a rectangular and an arbitrary-shaped loop.These elements produce a useful B₁ field normal to the plane defined bythe elements.

FIG. 2 shows a so-called “Figure-8”, a symmetric/asymmetric saddle, andan arbitrary-shaped crossed coil. They can be placed flat or conformedto some curvature. These elements produce a useful B₁ field parallel tothe plane defined by the elements.

FIG. 3 shows a so-called “Figure-8” train, a symmetric/asymmetric saddletrain, and an arbitrary-shaped crossed coil train. They can be placedflat or conformed to some curvature. These elements produce a useful B₁field parallel to the plane defined by the elements.

FIG. 4 shows a “ladder” coil or a “half-birdcage” coil if curved arounda volume of interest. The element has multiple resonant modes. Forexample, by exciting appropriate modes of the element, this coil cangenerate both a B₁ field normal to and a B₁ field parallel to the planedefined by the coil at the same imaging frequency. Other modes may beexcited depending upon the application of interest.

FIG. 5 shows a so-called “H” coil and is also a multi-mode coil.

FIG. 6 a shows an A-type mode-controlled loop pair coil (MCLP coil). TheB₁ magnetic field polarization depends upon how the cable is connectedto the coils.

FIG. 6 b shows a B-type mode-controlled loop pair coil (MCLP coil) shownin solid lines. The B-type MCLP coil is shown with a loop coil inphantom lines, constituting a quadrature coil. Thus, the B-type MCLPcoil functions as a well known “Figure 8” or saddle coil.

FIG. 6 c shows an AB-type mode-controlled loop pair coil (MCLP coil).The AB-type MCLP coil is independent of cable connection (polarity). Forthis to function, the cable becomes high capacitance (relative to 50ohms; large capacitance=comparable or greater than 50 ohms; smallcapacitance=much less than 50 ohms, e.g., 20 ohms).

FIG. 6 d shows a mode-controlled loop pair coil (MCLP coil). Byadjusting the cable length, the overlap area can be controlled. ThisMCLP coil functions as a “Figure-8” or saddle coil.

These coil configurations are combined into an array of smaller and morenumerous coils than was contemplated in the past.

Referring to FIG. 7, this is a coil array 10 where combinations ofquadrature ladder/half-birdcage coils 12, 14 are used together withloops coils 16, 18, 20, 22 whose sizes are optimized for S/N. Thequadrature ladder/half-birdcage coil sections may be replaced by “H”coils or a combination of loop and “Figure 8” (saddle) coils. Although aconfiguration where adjacent coils are overlapped is shown, overlappingis not necessary when a low-input impedance preamplifier decouplingtechnique is employed, for instance. In parallel imaging modality, theelements of a coil array should be smaller than for common phased-arrayimaging, resulting in a trade-off between basic noise and geometryfactor. Non-overlapping configuration may yield a net gain in S/N due tothe improved geometry factor when using SENSE.

Referring to FIG. 8, this is a coil array 24 where combinations ofdifferent type of quadrature coils (i.e., ladder/half-birdcage coils 26,28, a loop-and-butterfly quadrature coil 30 are used for giving distinctphase information together with loop coils 32, 34 whose sizes areoptimized for PPA applications and S/N. The ladder/half-birdcagesections may be replaced by “H” coils or a combination of loop and“Figure 8” (saddle) coils. Although a configuration where adjacent coilsare overlapped is shown, overlapping is not necessary when a low-inputimpedance preamplifier decoupling technique is employed, for instance.In parallel imaging modality, the elements of a coil array should besmaller than for common phased-array imaging, resulting in a trade-offbetween basic noise and geometry factor. Non-overlapping configurationmay yield a net gain in S/N due to the improved geometry factor whenusing SENSE.

Referring to FIG. 9, this is a coil array 36 where combinations ofquadrature ladder/half-birdcage coils 38, 40, 42, 44 are used. Thequadrature ladder/half-birdcage sections may be replaced by “H” coils ora combination of loop and “Figure 8” (saddle) coils. Although aconfiguration where adjacent coils are overlapped is shown, overlappingis not necessary when a low-input impedance preamplifier decouplingtechnique is employed, for instance. In parallel imaging modality, theelements of a coil array should be smaller than for common phased-arrayimaging, resulting in a trade-off between basic noise and geometryfactor. Non-overlapping configuration may yield a net gain in SNR due tothe improved geometry factor when using SENSE.

Referring to FIG. 10, this is a coil array 46 where combinations ofquadrature ladder/half-birdcage coils 48, 50 are used together withanother type of quadrature coils, namely, a combination of a loop and abutterfly coils 52, 54. The quadrature ladder/half-birdcage coils may bereplaced by “H” coils or a combination of loop and “Figure 8” (saddle)coils. The sizes of the loop and the butterfly coils are chosen suchthat B1 field penetrates deep enough so as to tissues at the centerregion can be imaged with high S/N. This applies to the quadratureladder/half-birdcage sections. Although a configuration where adjacentcoils are overlapped is shown, overlapping is not necessary when alow-input impedance preamplifier decoupling technique is employed, forinstance. In parallel imaging modality, the elements of a coil arrayshould be smaller than for common phased-array imaging, resulting in atrade-off between basic noise and geometry factor. Non-overlappingconfiguration may yield a net gain in S/N due to the improved geometryfactor when using SENSE.

Referring to FIG. 11, this is a coil array 56 where combinations ofquadrature ladder/half-birdcage coils 58, 60 are used together with loopcoils 61, 62, 63, 64. The quadrature ladder/half-birdcage sections maybe replaced by “H” coils or a combination of loop and “Figure 8”(saddle) coils. The sizes of the loop coils are optimized for S/N.Although a configuration where adjacent coils are overlapped is shown,overlapping is not necessary when a low-input impedance preamplifierdecoupling technique is employed, for instance. In parallel imagingmodality, the elements of a coil array should be smaller than for commonphased-array imaging, resulting in a trade-off between basic noise andgeometry factor. Non-overlapping configuration may yield a net gain inS/N due to the improved geometry factor when using SENSE.

Referring to FIG. 12, this is a coil array 66 where combinations ofquadrature ladder/half-birdcage coils 68, 70, 72 are used, each havingdifferent curvature and size for optimized S/N. The quadratureladder/half-birdcage sections may be replaced by “H” coils or acombination of loop and “Figure 8” (saddle) coils. Although aconfiguration where adjacent coils are overlapped is shown, overlappingis not necessary when a low-input impedance preamplifier decouplingtechnique is employed, for instance. In parallel imaging modality, theelements of a coil array should be smaller than for common phased-arrayimaging, resulting in a trade-off between basic noise and geometryfactor. Non-overlapping configuration may yield a net gain in S/N due tothe improved geometry factor when using SENSE.

referring to FIG. 13, this is a coil array 74 where combinations ofquadrature coils 76, 78, 80, 82 are used. A configuration where adjacentcoils are not overlapped is shown since this non-overlappingconfiguration yields better phase definition associated with each coil.A low-input impedance preamplifier decoupling technique ensures adequatedecoupling of neighboring coils (i.e., mutual inductance betweenadjacent coils are minimized). Traditional decoupling technique such asoverlapping adjacent coils is possible, too. In parallel imagingmodality, the elements of a coil array should be smaller than for commonphased-array imaging, resulting in a trade-off between basic noise andgeometry factor. Non-overlapping configuration may yield a net gain inS/N due to the improved geometry factor when using SENSE.

Referring to FIG. 14, this is a coil array 84 where combinations ofquadrature coils 86, 88, 90, 92 are used. The ladder/half-birdcagesections 86, 88 may be replaced for example, by “H” coils or acombination of loop and “Figure 8” (saddle) coils. A configuration whereadjacent coils are not overlapped is shown since this non-overlappingconfiguration yields better phase definition associated with each coil.A low-input impedance preamplifier decoupling technique ensures adequatedecoupling of neighboring coils (i.e., mutual inductance betweenadjacent coils are minimized). Traditional decoupling technique such asoverlapping adjacent coils is possible, too. In parallel imagingmodality, the elements of a coil array should be smaller than for commonphased-array imaging, resulting in a trade-off between basic noise andgeometry factor. Non-overlapping configuration may yield a net gain inS/N due to the improved geometry factor when using SENSE.

Referring to FIG. 15, this a coil array 94 for torso imaging. Anteriorpart 96 and posterior part 98 are made of differently sized loops forthe optimized S/N. They may be flat or curved. Loops shown in solidlines are positioned to optimize imaging of a region of interest, andthey may be overlapped for improved decoupling between adjacent loops ornon-overlapped for a net gain in S/N due to the improved geometry factorwhen using SENSE. Shown in dashed lines are saddle or “Figure-8” coils.When they are placed on top of the loops as shown in FIG. 14,improvement in SIR is achieved.

Referring to FIG. 16, this is a coil array 100 where combinations ofthree quadrature coils 102, 104, 106 (i.e., a loop coil and abutterfly/saddle/“Figure-8” coil) are used, each having differentcurvature and size for optimized S/N. Although a configuration whereadjacent coils are overlapped is shown, overlapping is not necessarywhen a low-input impedance preamplifier decoupling technique isemployed, for instance. In parallel imaging modality, the elements of acoil array should be smaller than for common phased-array imaging,resulting in a trade-off between basic noise and geometry factor.Non-overlapping configuration may yield a net gain in S/N due to theimproved geometry factor when using SENSE.

Referring to FIG. 17, a loop coil 108 in dashed lines and an MCLP coil110 shown in black constitute a quadrature coil 112 since the MCLP coilfunctions as a “Figure 8” or saddle coil. The cables connecting twoloops to form an MCLP coil can be 75 ohms or 50 ohms. Another pair ofthe loop-MCLP quadrature coil 114 is distributed in the z direction tocover a large FOV. The loop-MCLP quadrature coil can be distributedaround a human body not only in a circumambient direction (m=1, 2, 3, 4. . . ) but also in the z direction (n=1, 2, 3, 4 . . . ).

Referring to FIG. 18,: Two pairs of loop-saddle quadrature coils 116,118 are distributed in the z direction to form an anterior coil, andanother two pairs of the loop-saddle quadrature coils 120, 122 areplaced on a posterior coil. The “Figure-8” or saddle coils can bereplaced by MCLP coils.

It should be evident that this disclosure is by way of example and thatvarious changes may be made by adding, modifying or eliminating detailswithout departing from the fair scope of the teaching contained in thisdisclosure. The invention is therefore not limited to particular detailsof this disclosure except to the extent that the following claims arenecessarily so limited.

1. A partially parallel acquisition RF coil array for imaging a sample,said array comprising: at least a first, a second and a third coil, saidfirst, second and third coils each extending partly circumambientlyaround a portion of a single radial region to be imaged and togethersaid first, second and third coils forming a single coil array extendingcircumambiently around said single radial region of the sample, saidcoil array configured to provide both contrast data and spatial phaseencoding data.
 2. An array of RF coils according to claim 1, wherein atleast two of said coils are quadrature coils.
 3. An array of RF coilsaccording to claim 1, wherein said coils are quadrature coils.
 4. Anarray of RF coils according to claim 1, wherein said coils arequadrature ladder/half-bird cage coils.
 5. An array of RF coilsaccording to claim 1, wherein said coils are quadratureloop-and-butterfly coils.
 6. An array of RF coils according to claim 1,further comprising a fourth, a fifth and a sixth coil in saidcircumambient arrangement, wherein said first and second coils arequadrature ladder/half-bird cage coils and said third, fourth, fifth andsixth coils are loop coils.
 7. An array of RF coils according to claim1, further comprising a fourth and a fifth coil in said circumambientarrangement, wherein said first and second coils are quadratureladder/half-bird cage coils and said third and fourth coils are loopcoils, and said fifth coil is a quadrature loop-and-butterfly coil. 8.An array of RF coils according to claim 1, further comprising a fourthcoil in said circumambient arrangement, wherein said first, second,third and fourth coils are quadrature ladder/half-bird cage coils.
 9. Anarray of RF coils according to claim 1, further comprising a fourth coilin said circumambient arrangement, wherein said first and second coilsare quadrature ladder/half-bird cage coils and said third and fourthcoils are quadrature loop-and-butterfly coils.
 10. An array of RF coilsaccording to claim 1, further comprising a fourth coil in saidcircumambient arrangement, wherein said first, second, third and fourthcoils are quadrature loop-and-butterfly coils.
 11. An array for parallelimaging comprising: a plurality of coils each extending partlycircumambiently around a portion of a single radial region of a sampleto be imaged, said plurality of coils providing contrast and spatialphase encoding data, said plurality of coils configured to be arrangedin combination as a single coil array, and said plurality of coilsforming a single coil array extending circumambiently around said singleradial region.
 12. An array according to claim 11, wherein at least twoof said plurality of coils comprise quadrature coils.
 13. An arrayaccording to claim 11, wherein at least two of said plurality of coilscomprise quadrature ladder/half-bird cage coils.
 14. An array accordingto claim 11, wherein at least two of said plurality of coils comprisequadrature loop-and-butterfly coils.
 15. An array according to claim 11,wherein said plurality of coils comprise at least three coils configuredto be arranged in combination circumambiently about a sample.
 16. Anarray according to claim 11, wherein said plurality of coils comprise atleast two sets of three coils, each set configured to be arranged incombination circumambiently about a sample.
 17. An array according toclaim 11, wherein at least two of said plurality of coils areoverlapping.
 18. An array according to claim 11, wherein said pluralityof coils are non-overlapping.
 19. A method for parallel imagingcomprising: arranging a plurality of coils in combination as a coilarray such that each of the plurality of coils is configured to extendpartially circumambiently around a portion of a single radial region ofa sample, said coils together extending circumambiently around saidsingle radial region.
 20. A method according to claim 19, wherein saidarranging comprises forming a single circumambient array of coils.